It isn't unusual for building materials, both inside a home as well as outdoors, to expand and contract with changes in temperature and humidity. It's actually a natural process that occurs over time. But astute builders and installers know how to compensate for these inevitable shifts.
Installing tiles, particularly in moist environments like bathrooms and kitchens, requires that particular attention be paid to expansion and contraction in floor tiles and the plywood subfloor beneath them.
For instance, the heat generated by bathroom floor heating, which operates from the surface rather through air ducts, is a factor that installers should consider. Radiant floor heating has become so popular for its energy efficiency and its uniform warming that more professionals are trained to take heated tile floors into account when they begin an installation job.
The last thing that tile contractors - and the homeowners that hire them - want to see happen is a condition called "tenting," which occurs if tiles press against each other and pop up from the floor in a tent formation. But proper preparation and installation can prevent this from happening.
Vancouver general contractor John Whipple advised homeowners to avoid large-format tile because having more grout joints that occur with smaller tiles allows for minor movement and spreading out. This is an important issue in large bathrooms that get lots of natural light from large windows because they absorb more heat and can cause more tile expansion than usual. Dark-colored tiles should be avoided in large bathrooms for the same reason.
Consider the Subfloor
In his column for Houzz.com, Whipple also warned installers to prevent too much dust, debris or the adhesive mortar, or "thinset," from settling on the subfloor because it will prevent the surface from moving if the joints are mortared in too tightly. For instance, there should be no thinset where the tile meets the wall because the tile floor needs this space to move and expand. Tenting will result otherwise.
On the other hand, using too little thinset may cause failure in the tile bonding. A telltale sign of insufficient thinset is a hollow noise that occurs when you walk across the newly tiled floor. Whipple offered this tip: Use the wooden handle of a rubber mallet to gently tap set tiles. This will help homeowners find the hollow noise that indicates there hasn't been enough thinset applied to ensure a strong bond.
This Old House magazine recommended that homeowners and installers could save themselves some headaches by planning a tiling job well from the outset. For instance, the floor layout should use as many whole tiles as possible, minimizing the need to cut more tiles than necessary. Awkward-sized tiles should be placed where vanities will cover them or at least out of the sight lines from the doorway.
By saving all the tile cutting until the end of a job, a wet saw that has to be rented can be used for a shorter period of time.
A special form of thinset is needed for steam showers because of the powerful heat and intense moisture. Since glass expands more than most building materials, the glass around the shower can contribute to the problem.
To compensate, Whipple suggested that two layers of a waterproofing membrane be used in the corners of the shower stall.
In very large bathrooms, using expansion strips in the tile assembly provides more stability to the tile. In expanses that are more than 15 feet in one direction, an expansion strip along with specialty thinset and grouts for such situations will provide better expansion capability and prevent mortar failure.